For operating lighting devices, the manufacturer determines a voltage so called rated voltage and keeping and maintaining this voltage the parameters given by the manufacturer for said lighting source are warranted. From the light emitted by the light source in the visible spectrum of light, and measured by a photometer being made according to CIE standards, can be determined the radiated power, further on the output light power.
EP 0807311 describes a device for uninterrupted voltage control with an autotransformer where at least one switching element 11 is connected in the primary circuit 2 of the transformer for switching out and at least one further switching element 9 is connected in the primary circuit 2 of the transformer or connected parallel with the secondary circuit coupled to the consumer. In case the voltage on the consumer should be switched over switching elements 9, 11 are controlled so that the secondary coil 13 operates as choke. The aim of the invention is to realize the operation with an uninterrupted switch over. No teaching can be found regarding the increase of the illumination effect and regarding the special measure of the transformer.
WO2006/028781 describes a device for control the operation of discharge lamps. The circuit arrangement is similar to the device described in EP 0807311. The aim of this invention is written in lines 17-22 and lines 25-27 on page 5. Accordingly the transition from full voltage to a reduced voltage occurs without an interruption of the current flow to the lighting unit. There is also a thermal analog device 36 to insure that the lighting unit can remain lighted when the voltage level is reduced for sustained operation. EP2 107 861 and DE 298 1722 both describe supply units for changing voltage on a consumer without interruption of the supply voltage.
According to prior art it is known that in the case of fluorescent lighting devices a 15-20% reduction in the power supply related to the rated voltage results in a smaller decrease in the output lighting power than in the electric power. In case of reduction in the electric power by 25-35%, typically by 25%, the output lighting power decreases by 10-25%, typically by 20%.
It is also known that a reduction of the power supply by 15-20% results in increase of the life time of fluorescent lighting devices by 1.5-2.5 times.
There are devices available in the commercial market solving the problem of decreasing lighting energy by reducing the supply voltage. In these devices transformers are applied the iron core and the copper coils of which together represent a significant mass and the transformer is bulky. In transformers, the idle voltage i.e. the voltage without any load might be different from the voltage when the transformer is connected to a load. The difference can be even 40-50%. The energy for supplying the consumer passes the transformer through an inductive coupling.
There are solutions known from the prior art using an AC electromechanical voltage control device. The principle of this solution is that the change of the input voltage is controlled automatically by a transformer coupled in series with the load and supplied through another transformer having variable ratio so that the output voltage should always be at the appropriate level. The main draw-back of this solution is that it contains mobile elements for varying the ratio of the transformer. Such a solution is published in the patent specification. CN 1 122967. In this solution, the secondary coil of a transformer is coupled in series to the consumer, whereas by an appropriate tapping and controlling of the primary coil, the voltage of the secondary coil can be changed within a wide range.
The price of a transformer for a given power is reimbursed at general use in about two years, thus the expected profit remains low.
A further method known from the prior art is when in bureau-houses or in separate lighting units, a part of the whole system is lightened only, a central step-down transformer provides a higher voltage to the whole system in order to help starting the part of the system to be switched-on. Sensing that the circuit for lighting a part of the whole system being switched-on cab be solved by replacing each switch of the lighting system for quadripole switches. Two poles of each switch serve the switching on of the lighting circuit, two transmit the information on switching-on to the central unit through a wiring built out for this purpose. The construction of the system requires a lot of supplementary work. In addition to replacing the switches, two wires should be arranged to the central unit from each switch. This work is complicated and needs wall drilling and wiring. Working costs of building and placing the supplementary elements are high without considerable saving the return time of the project is definitely more than two years.
There are also several control devices having AC voltage control transformers known form the prior art. The secondary coil of the transformer is coupled in series between the power supply and the load, the primary coil of the transformer is connected to the supply voltage. The device comprises also switches for either exciting the primary coil from the input voltage, or short-circuiting the primary coil by semiconductor switches. The device can provide lower and higher voltages as well, corresponding to the state of the semiconductor switches. After switching, the switches are high loaded due to the inductivity of the inductive elements, i.e. the primary and secondary coils. In the moment of switching, instantaneous pulses of 1000 V or higher may occur. This represents a remarkable load on the semiconductors leading to a quick damage. The deviation from the standard rated voltage of 350 V is very large, besides its occurrence is seldom and random.